1. Field of the Invention
Aspects of the invention relate to a phase detecting device, a phase control device including the phase detecting device, and a fuser control device including the phase control device. More particularly, aspects of the invention relate to a phase detecting device that accurately detects zero-crossing points of an alternating current (AC) voltage in a normal mode, and reduces electric power consumption in a standby mode, a phase control device including the phase detecting device, and a fuser control device including the phase control device.
2. Description of the Related Art
An image forming apparatus, such as a printer, a photocopier, a facsimile machine, and a multifunction device combining the functionality of several different pieces of office equipment into a single machine, is a device for printing an image on a print medium by executing a print operation corresponding to input data.
Generally, an image forming apparatus requires a heating device in order to execute a print operation properly, and a device for maintaining the temperature of such a heating device at a predetermined temperature. A fuser for fixing a toner image formed on a print medium requires a fuser control device in order to maintain the surface temperature of the fuser at a predetermined temperature appropriate for the toner image to be fixed on the print medium.
A phase controlling method for controlling AC input power has been extensively used in a fuser control device in the related art. In order to apply the phase controlling method, a phase detecting device for detecting zero-crossing points of an AC input voltage is required. Zero-crossing points of an AC voltage are points where the waveform of the AC voltage crosses a zero voltage level as the polarity of the AC voltage changes from positive to negative, or from negative to positive.
FIG. 8 is a circuit diagram of an example of a phase detecting device according to the related art.
Referring to FIG. 8, a phase detecting device 10 includes a power input unit 12 through which an AC voltage is input, and a phase detecting unit 14.
The power input unit 12 includes resistors R21, R22, R23, and R24 which divide the AC voltage and output a divided AC voltage.
The phase detecting unit 14 includes a first phase detector 14-1 and a second phase detector 14-2 which detect zero-crossing points of the AC voltage according to positive and negative polarities of the AC voltage based on the divided AC voltage outputted from the power input unit 12. That is, the first phase detector 14-1 detects zero-crossing points of a positive polarity of the AC voltage, and the second phase detector 14-2 detects zero-crossing points of a negative polarity of the AC voltage.
The first and second phase detectors 14-1, 14-2 include photocouplers including first and second light-emitting elements D11, D12 activated by the divided AC voltage to emit light, and first and second light-receiving elements PT11, PT12 respectively corresponding to the first and second light-emitting elements D11, D12 which are connected to an external DC voltage (Vcc11) through a resistor R25 and are activated in response to the light emitted from the first and second light-emitting elements D11, D12.
The phase detecting unit 14 further includes a switching element TR11 which is connected to the external DC voltage (Vcc11) through a resistor R26 and is turned on and off according to the activation of the first and second light-receiving elements PT11, PT12.
The operation of the phase detecting device shown in FIG. 8 according to the related art will now be described.
FIG. 9 is a diagram for explaining the operation of the phase detecting device shown in FIG. 8 according to the related art.
Referring to FIGS. 8 and 9, an AC voltage is input and divided through the power input unit 12, and alternately flows into the first and second phase detectors 14-1, 14-2. That is, the positive polarity of the divided AC voltage flows into the first phase detector 14-1, and the negative polarity of the divided AC voltage flows into the second phase detector 14-2.
For instance, a positive AC voltage is inputted to the first light-emitting element D11 of the first phase detector 14-1, and activates the first light-receiving element PT11. Since the first light-receiving element PT11 is activated by the AC voltage, a current path is formed between the external DC voltage (Vcc11) and a ground voltage (indicated by an inverted triangle in the FIG. 8) through the resistor R25 and the first light-receiving element PT11, thereby causing a voltage of a first node N11, at which the external DC voltage (Vcc11) is connected to the first light-receiving element PT11 through the resistor R25, to be the ground voltage.
Accordingly, the switching element TR11 is turned off, thereby causing a voltage of a second node N12, at which the external DC voltage (Vcc11) is connected to the switching element TR11 through the resistor R26, to be the DC voltage (Vcc11). While the polarity of the AC voltage is positive, the voltage of the second node N12 is outputted as a phase detecting signal (Vphase).
The first and second phase detectors 14-1, 14-2 are deactivated at a zero voltage, or a voltage close to the zero voltage, due to the voltage sensitivity of the first and second phase detectors 14-1, 14-2. As a result, the phase detecting signal (Vphase) outputted from the second node N12 is outputted as a pulse signal as shown in FIG. 9.
Meanwhile, it is preferable to reduce a power consumption of the phase detecting device 10 by preventing the device from operating when the device does not detect the zero-crossing points, such as when there is no need for the fuser to maintain the predetermined temperature, such as when the image forming apparatus is in a standby mode. However, the phase detecting device 10 of FIG. 8 operates even in the standby mode, thereby causing a large amount of power consumption by the resistors R21, R22, R23, and R24 of the power input unit 12.
Differences in performance of the first and second phase detectors 14-1, 14-2 in detecting the zero-crossing points of the positive and negative polarities the AC voltage occur due to variations in manufacturing and differences in sensitivity of the first and second light-emitting elements D11 and D12 and the first and second light receiving elements PT11, PT12. Thus, a pulse width P1 of the phase detecting signal (Vphase) shown in FIG. 9 which is generated by the second light-emitting element D12 and the second light-receiving element PT12 for a negative polarity of the AC voltage may differ from a pulse width P2 of the phase detecting signal (Vphase) shown in FIG. 9 which is generated by the first light-emitting element D11 and the first light-receiving element D12 for a positive polarity of the AC voltage, which may cause nonuniformities in performing phase control based on the phase detecting signal (Vphase) with respect to the positive and negative polarities of the AC voltage.